1. Technical Field
The present invention relates to an electronic circuit having an electronic component mounted on a substrate, a light source device having the electronic circuit, and a method of manufacturing the electronic circuit on which the electronic component is mounted on the substrate.
2. Description of the Related Art
In general, an electronic component includes a lead pin as a connecting terminal. In the case in which an electronic circuit is fabricated by using the electronic component in plural, the electronic components are mounted on a substrate.
As a method of mounting an electronic component on a substrate, for example, there is known through-hole mounting. Referring to the through-hole mounting, lead pins of an electronic component are inserted into a through hole provided corresponding to the positions and number of the lead pins in a mounting position on the substrate and are fixed by soldering or the like.
In recent years, the need for mounting electronic components on an electronic circuit at a high density is increasing. For example, in some laser diodes (hereinafter referred to as “LDs (Laser Diodes)” according to an example of the electronic component, a plurality of light emitting elements are disposed in a single component and irradiation can be thus carried out with a plurality of beams, that is, so-called multibeams. In a laser diode array (hereinafter referred to as an “LDA (Laser Diode Array)”) capable of carrying out the irradiation with the multibeam, lead pins corresponding to the light emitting elements are arranged circumferentially at a small interval.
In the case in which the LDA is through-hole mounted on a substrate, it is necessary to form a plurality of through holes on the substrate at a small interval. In the case in which the LDA is through-hole mounted on the substrate, moreover, it is necessary to insert the lead pins in through holes, thereby soldering them.
In order to insert the lead pins in the through holes provided at the small interval, it is conceivable to increase diameters of the through holes for easy insertion of the lead pins.
In order to easily insert the lead pin into the substrate, generally, it is desirable to form a through hole having a size which is at least four times as large as a lead pin diameter.
In this case, however, it is necessary to increase the number of the lead pins and to reduce a pitch. When through holes each having an enough size with respect to the lead pin diameter are to be formed on the substrate, adjacent through holes are thinned and caused to be broken, so that the through holes cannot be formed.
In the case in which the lead pins are inserted into the through holes provided at the small interval, moreover, it is conceivable to change shapes of the lead pins (forming), thereby increasing a pitch between the lead pins. By carrying out the forming over the lead pins, it is possible to easily carry out attachment by increasing the interval among the through holes on the substrate.
Also in this case, however, the lead pin diameter of the LDA is 0.3 mm, for example, which is smaller than a lead pin diameter, 0.45 mm for example, of an LD in the related art. In other words, the lead pin of the LDA tends to be deformed by external force. In the case in which the LDA is mounted on the substrate, accordingly, even if the lead pin has been subjected to the forming, it is hard to maintain a state at the forming while guiding the lead pin to the substrate.
In the case in which the LDAs are mounted in the same substrate, moreover, it is impossible to ensure an enough pitch between the lead pins for obtaining an advantage in the attachment even if the forming is performed because the attachment intervals among the LDAs are close to each other due to optical limitations.
In order to mount the LDAs at a small interval in the same substrate to increase printing speed and definition, furthermore, it is necessary to cause a beam interval in a sub-scanning direction to be uniform, that is, to perform so-called pitch adjustment between sub-scanning beams before assembling the LDAs onto the substrate.
In place of the method of manufacturing an electronic circuit by forming a through hole and mounting an electronic component, therefore, there is known a method of manufacturing an electronic circuit by providing a single large hole on a substrate with respect to a single electronic component and soldering a lead pin of the electronic component to the substrate, for example, as described in Patent Document 1 (Japanese Patent Application Registration No. JP-2638953-B1, that is, JP-H02-23540-A), Patent Document 2 (Japanese Patent Application Publication No. JP-H07-154046-A), and Patent Document 3 (Japanese Patent Application Publication No. JP-2006-072136-A).
FIG. 1 is a sectional side view showing an electronic circuit 100 according to the related art. As shown in FIG. 1, in the case in which the electronic circuit 100 is manufactured by using the technique of Patent Document 1, a hole 11 is formed on a substrate 10. The hole 11 has a larger diameter than a diameter of a circumference (hereinafter referred to as a “lead pin circle diameter”) of a position in which lead pins 21 of an LDA 20 are disposed.
Referring to the technique of the Patent Document 1, the lead pins 21 are caused to pass through the hole 11 and are fixed by a solder 30 at an opposite surface (hereinafter referred to as a “back face”) to a surface of the substrate 10 on which the LDA 20 is mounted.
Referring to the techniques of Patent Document 2 and Patent Document 3, moreover, the lead pin 21 is bent along the back face of the substrate 10 and is thus fixed by a solder 30a. 
Referring to the technique of the Patent Document 1 shown in FIG. 1, however, wraparound of the solder 30 toward the hole 11 side with respect to the lead pin 21 is insufficient and a solder fillet is formed insufficiently as compared with a method of soldering the lead pin passing through the through hole. For this reason, the technique of the Patent Document 1 lacks reliability of the fixing state of the LDA 20.
FIG. 2 is another sectional side view showing the electronic circuit according to the related art. In the case in which the lead pin 21 is bent along the back face of the substrate 10 and is thus fixed by the solder 30a as in the Patent Document 2 and the Patent Document 3, there is generated a so-called solder bridge in which the adjacent solders 30a come in contact with each other as shown in FIG. 2 if a distance C between the leads representing an interval between adjacent LDAs 20 is reduced. In the techniques of the Patent Document 2 and the Patent Document 3, therefore, it is impossible to mount the LDA 20 at a small interval.